computeCentroids  <- function(X, idx, K) {
  
  #   returs the new centroids by computing the means of the
  #   data points assigned to each centroid.
  #
  #   centroids <- computeCentroids(X, idx, K) returns the new centroids by
  #   computing the means of the data points assigned to each centroid. It is
  #   given a dataset X where each row is a single data point, a vector
  #   idx of centroid assignments (i.e. each entry in range [1..K]) for each
  #   example, and K, the number of centroids. You should return a matrix
  #   centroids, where each row of centroids is the mean of the data points
  #   assigned to it.
  #
  
  # Useful variables
  m <- dim(X)[1]
  n <- dim(X)[2]
  
  # You need to return the following variables correctly.
  centroids <- matrix(0, K, n)
  
  
  #  ======================== YOUR CODE HERE ========================
  # Instructions: Go over every centroid and compute mean of all points that
  #               belong to it. Concretely, the row vector centroids[i, ]
  #               should contain the mean of the data points assigned to
  #               centroid i.
  #
  # Note: You can use a for-loop over the centroids to compute this
  #

  
  # ==============================================================
  return(centroids)
}